Conventionally, a common arrangement for mounting an axle of many heavy trailers provides that the chassis or frame of the vehicle is furnished with brackets on both sides of the trailer on each of which an axle-carrying arm is mounted. The arms pivot about a common horizontal axis parallel to the axle. A spring system is mounted between each arm (or each end of the axle) and the chassis. The spring system may comprise a mechanical spring or an air cushion or piston-and-cylinder arrangement. In any case the arrangement allows the axle to ride up and down non-reactively relative to the chassis pivoting with the arms about the common axis. Because as a matter of practicality one end of the axle will often ride to a higher or lower position relative to the chassis than the other end, it is necessary to allow for a degree of flexibility in the joints between the axle and the arms and/or between the arms and the mounting brackets on the chassis. Commonly this flexibility is achieved by providing a rubber bush between the components at the joints in question. Conventionally the rubber bush comprises inner and outer cylindrical metal sleeves coaxially located with an annular body of rubber in the space between the sleeves. The bush is mounted on the bracket by means of a bolt which passes through the inner sleeve and clamps the bush to the bracket. The axle arm is fixed to the outer sleeve in some suitable manner, as for example by means of a caliper-shaped clamp which passes around the outer sleeve and is bolted to the end of the arm.
Conventionally, the bushes are manufactured by press-fitting the rubber body to the sleeves. Because this requires special machinery known such bushes are expensive and it is one object of the invention to provide a bush in which the press-fitting operation is eliminated.
Proposals have also been made to provide a bush for flexibly joining two components together in which the rubber body is not pressed into inner and outer sleeves. Instead the bush can be inserted in a socket formed in one of the components and expanded into frictional contact with the socket when the other component is mounted. One proposed means of achieving this expansion is to provide the rubber bush with a tapered bore and to provide a complementally tapered bolt or pin for mounting the other component, the bolt being inserted in the bore and forcing the rubber body radially outwardly during the mounting process. Another means of achieving the expansion which has been suggested is to squeeze the rubber body inwardly in the axial direction means of washers located at each end thereof, the washers being pulled towards one another when a nut mounted on the bolt is tightened up. Examples of bushes of these kinds (non of which are intended for suspensions comprising an axle carried on a rigid trailing arm) are disclosed in U.S. Pat. Nos. #3,434,707, #242,950, #2,346,574, #3,989,126 and #3,493,222.
It is a further problem with suspensions, particular of heavy vehicles, that it is laborious and time consuming to mount the axle-carrying arm on the frame due to misalignment between the bore of the bush and the holes in the frame which receive the bolt which is inserted in the bore. This problem may arise for various reasons the most common being distortion of the frame of the vehicle as a result of an accident. The above mentioned U.S. Pat. No. #3,434,707 discloses a system for bringing the bore of the bush into alignment with the holes in the frame. This system comprises essentially the provision of additional bushes which are inserted in the holes in the frame. These additional bushes are provided with holes for the bolt which holes are bored off centre so that rotation of the bushes will bring the holes therein into line with the bore of the rubber rubber.
In the applicant's view the arrangement disclosed in U.S. Pat. No. #3,434,707 suffers from several disadvantages. First, it is complex and therefore expensive. Second, there will inevitably be rapid wear between the aforementioned washers and the nuts which bear on the them. Related to this is the fact that the bore of the rubber bush is provided with a metal sleeve and the bush is free to rotate about the bolt which passes through the bore. Some of the dampening effect of the rubber bush is thus lost. Third, the provision of two separate bushes with off centre holes appears likely to complicate the process of lining up the bore of the bush with the off centre holes. trailer provided with a suspension comprising an axle mounted on a rigid trailing arm.